Fastener driving apparatus

ABSTRACT

The invention concerns a fastener-driving apparatus comprising a tank ( 8 ) for storage of a fuel, in particular a liquefied gas, a combustion chamber ( 4, 5 ) connected to the tank ( 8 ) via a valve element ( 9 ), where the combustion chamber ( 4, 5 ) has a movable piston ( 3 ) to advance a driving ram ( 2 ), and an ignition device for ignition of an air-fuel mixture in the combustion chamber, where an injection line ( 10, 11, 12 ) is provided between the tank ( 8 ) and the combustion chamber ( 4, 5 ), where the injection line ( 10, 11, 12 ) has optimization with regard to an expansion and/or transport time.

The invention concerns a fastener-driving apparatus, in particular a hand-operated driving apparatus, according to the generic part of Claim 1.

U.S. Pat. No. 4,712,379 describes a combustion gas-driven fastener-driving apparatus in which liquefied gas is sent to a combustion chamber from a supply tank via a gas line. After injection of an amount of combustion gas into the combustion chamber, which is filled with air, ignition of the combustion gas-air mixture can take place in order to advance a piston with a connected driving ram to drive a fastening element, for example a nail.

Frequently, such devices are operated with liquefied gas, where an amount of the gas, which is in liquid phase and under pressure, is first introduced into the line to the combustion chamber via a valve element. A certain amount of time passes before there is sufficient—and as complete as possible—evaporation of the liquefied gas and mixing with the combustion air, which can be a disruptive delay in the operation of the driving apparatus. The release of the combustion gas from the supply tank in this case usually does not take place until the driving apparatus has been pressed against a workpiece, through which pressing a safety mechanism is actuated. Because the period of time that elapses between said release of gas and the ignitability of the mixture is too long, there is the danger that the user will set down the apparatus or that it will be triggered as it is being set down.

It is the task of the invention to specify a fuel-driven driving apparatus the operation of which is improved by particularly short delay times.

This task is solved in accordance with the invention for a driving apparatus of the kind mentioned at the start with the characterizing features of claim 1. Through a thermally conductive element, the introduction of heat into the fuel is accelerated and the amount of delay time until formation of an ignitable mixture in the fuel chamber due to the fuel line is reduced. To further accelerate the introduction of heat into the fuel, the injection line is preferably in thermal contact with an outer wall of the combustion chamber. Especially preferably, the injection line contacts the outer wall of the combustion chamber.

In a preferred embodiment the heat-conducting element comprises a wall segment that extends outwardly and/or inwardly from an outer wall of the injection line. Especially preferably, the wall section is in thermal contact with the outer wall of the combustion chamber. Preferably, the wall section extends along the injection line.

In a preferred embodiment the injection line has two or more flow chambers for the fuel, which are separated from each other by the wall section. Especially preferably, the flow chambers are only separated from each other by the wall section.

In a preferred embodiment of the invention, it is provided that the optimization of the injection line is at least partially formed of a highly thermally conductive material, in a preferred development having a thermal conductivity of more than 70 W/(m·K). In particular, when the fuel for the driving apparatus is a liquefied gas that enters the injection line in liquid phase and must undergo phase conversion before ignition of the mixture in the combustion chamber, the heat to be delivered to the fuel is relatively high. In order to ensure this in a sufficiently short time, high thermal conductivity of the injection line is particularly advantageous. It turned out that the lines known from the prior art are made of steel, stainless steel, or even plastic. These materials have particularly low coefficients of thermal conductivity and therefore are not very suitable for accomplishing evaporation of liquefied gas or other fuel in the injection line.

In an especially preferred detailed design the injection line is made of copper. In each case according to the purity of the copper material, such an injection line can have a coefficient of thermal conductivity between around 250 and 400 W/(m·K), typically 350-370 W/(m·K). Basically, however, other highly heat-conductive materials are also conceivable, for example aluminum, brass, or other materials the thermal conductivities of which are considerably higher than those of steel or plastic.

In an alternative or supplemental embodiment of the invention it is provided that the injection line have, at least segment-wise, a plurality of branchings. In the case of a single injection line with a simple cylindrical form with smooth wall, which is known from the prior art, the inner surface of the injection line that can heat the combustion gas is relatively small in relation to the volume of the injection line.

In a preferred detailed design of the invention at least two of the branch lines are formed as segments of a line with a number of chambers. In this case, introduction of heat from outside into the fuel that is being passed through the segments is improved by the walls of the segments within the line. Such segmented lines can be produced in various known ways, for example from several metal sheets or even as extruded profiles.

In an alternative or supplemental development, at least two of the branch lines can be formed as separate lines, which preferably, but not necessarily, are spatially separated. Because of this, the space required for the line within the driving apparatus becomes larger and this also increases the material cost, but nearly any desired optimization of the heat input while at the same time having rapid transport of the fuel through the lines with small line volume can take place.

Especially preferably, at least one of the separate branch lines can be in thermal contact with an outer wall of the combustion chamber. In a useful combination of the features, a plurality of the branch lines is spatially separated and each is in thermal contact with different regions of the outer wall, so that an especially optimized heat transfer of the waste heat of the outer wall of the combustion chamber into the fuel supply lines can take place.

In another alternative or supplemental embodiment of the invention it can be provided that the separate branch lines enter the combustion chamber at separate places. This already supports better distribution of the fuel in the combustion chamber from the point of injection, so that an ignitable mixture can be achieved even faster. Especially preferably, to improve the turbulence of the injected fuel it can be provided that jets of fuel injected by the branch lines into the chamber cross each other. Through the meeting of at least partially gasified fuel at high velocity there is especially good turbulence due to the collision of the fuel molecules, aerosol droplets, and other components of the fuel jet.

According to a preferred embodiment example the thermally conductive element is arranged downstream from the valve element. Especially preferably, an insulation element is arranged between the valve element and the thermally conductive element. Premature evaporation of the fuel before or in the valve element, which could under certain circumstances distort the metering of the valve element, is suppressed or avoided. The insulation element can be formed in particular by a line segment of the fuel line made of a heat insulating material, for example a plastic, rubber, and/or silicon hose.

Other advantages and features of the invention result from the embodiment examples described below and from the dependent claims.

A number of embodiment examples of the invention are described below and explained in more detail by means of the attached drawings.

FIG. 1 shows a schematic overall view of a first embodiment example of a fastener-driving apparatus in accordance with the invention.

FIG. 2 shows a cross section through an injection line in accordance with another embodiment example of the invention.

FIG. 3 shows a wall of the injection line from FIG. 2.

The hand-operated fastener-driving apparatus shown in FIG. 1 comprises a housing 1, in which a driving ram 2 to drive nails, screws, rivets or other fastening elements (not shown) from a magazine 3 into a workpiece is accommodated. The driving ram 2 is connected at the end turned away from the workpiece to a piston 3, which is held in a cylinder 4 so that it can slide. Cylinder 4 is the continuation of or a part of a combustion chamber 5, which can be vented via a movable sleeve 6. In addition in combustion chamber 5 there is a fan 7, which is driven by a fan motor 7 a and which enables better mixing of fuel with combustion air.

In addition, in chamber 5 there is an ignition device (not shown), which can be triggered by an actuation switch 14 arranged on the handle 1 a of housing 1.

In its basic function, it is thus a fastener-driving device, in which the driving ram 2 is advanced to drive nails via piston 3 by ignition of a fuel-air mixture in combustion chamber 5.

The fuel is stored in a tank 8 in a lower region of housing 1. The fuel is a liquefied gas, for example propane or other suitable gas. Tank 8 is thus a pressurized storage tank. It can be made as a refillable tank that is fixed in place and permanently arranged in housing 1, as an exchangeable cartridge, or the like. Tank 8 is connected to a valve element 9 via a line segment 8 a, where dispensing of the liquefied gas to flow into combustion chamber 5 is provided via valve element 9.

Between valve element 9 and combustion chamber 5 there extends an injection line 10. Because of the relationship of pressure and flow, the liquefied gas is as a rule present in liquid phase not only in tank 8, but also up to valve element 9 and in line 8 a. Through the opening of valve element 9 the liquefied gas then undergoes a drop of pressure, so that the operation of evaporation of the liquefied gas in the course of dispensing or injection into fuel chamber 5 is already taking place in the entire injection line 10.

For optimization of the timing of evaporation of the liquefied gas in injection line 10, it is hydraulically divided into a first separate branch line 11 and a second separate branch line 12, which are spatially separate from each other, in at least one segment between valve element 9 and combustion chamber 5, especially at a distance from valve element 9.

The branch lines 11 and 12 open into the combustion chamber 5 at opposite, spatially separate positions. The orientation of the openings of the branch lines 11 and 12 is made such that the injected jets of liquefied gas cross or collide with each other in the combustion chamber. Better turbulization and faster evaporation in combustion chamber 5 is achieved through this.

In particular, the branch lines 11 and 12 can be brought into thermal contact with an outer wall of the combustion chamber 5 or the cylinder 4 or 5 as they go to combustion chamber 5. Through this, waste heat from the combustion chamber 4 and 5 can be released to the branch lines 11 and 12, so that evaporation within branch lines 11 and 12 is improved.

Branch lines 11 and 12 branch in a branching piece 13 from the first segment of the injection line 10. Of course, according to construction type the branch lines 11 and 12 can begin immediately at valve 9.

FIG. 2 shows an embodiment example of the invention in which the injection line 10 is formed as a segmented line with two chambers 10 a and 10 b. Here, the line 10 has a circular cross section of its outer circumference, with segments 10 a and 10 b each being essentially formed as semicircles. Line 10 comprises an outer, hollow cylindrical conduit casing 14, and each of segments 10 a and 10 b has its own casing of sheet material 15. Alternatively, the segmented injection line 10 can also be formed in one piece, for example as an extruded profile. One segment can also be present with the other as a circular outer cross section; in particular, the line can have a rectangular or square outer cross section. Formation of the line as a flat tube with a plurality of adjacent chambers or channels, for example as is known from the construction of heat exchangers, is also conceivable.

In a modification of the segmented injection line 10 according to FIG. 3, there are not just two chambers 10 a and 10 b, but rather three chambers 10 a, 10 b and 10 c, while the injection line 10 otherwise has the same design.

It is basically true for the embodiment examples according to FIG. 2 and FIG. 3 that the segmenting of the injection line 10 into a plurality of channels 10 a, 10 b and 10 c produces an improvement of the evaporation of the liquefied gas within the injection line 10. This occurs due to, among other things, the larger contact surface for the liquefied gas with the thermally conductive walls of channels 10 a, 10 b and 10 c. It is also conceivable that a segmented line in accordance with the invention is formed as a bundle, for example a twisted bundle of a number of separate thin lines with circular internal cross section. Such a line can be divided into a number of spatially separated paths of the individual thin lines, particularly in the course of guiding them in housing 1.

In an especially preferred embodiment of the invention, the injection line 10 or the branch lines 11 and 12 are made of a highly thermally conductive material, for example copper. The use of a highly thermally conductive material, preferably copper, for the injection line is preferably combined with any of said physical embodiments of the injection line 10, 11, 12.

In general, the individual features of the embodiment examples described above can be combined with each other in each case according to requirements. 

1. A fastener-driving apparatus comprising a receptacle for a tank for storing a fuel a combustion chamber that can be connected to the tank via a valve element where the combustion chamber has a movable piston to advance a driving ram and an ignition device for ignition of an air-fuel mixture in the combustion chamber, and an injection line provided between the tank and the combustion chamber, where the injection line has a thermally conductive element.
 2. The driving apparatus as in claim 1, wherein the injection line is in thermal contact with an outer wall of the combustion chamber.
 3. The driving apparatus as in claim 1, wherein the thermally conductive element comprises a wall segment, which extends outwardly from an outer wall of the injection line.
 4. The driving apparatus as in claim 3, wherein the wall segment extends along the injection line.
 5. The driving apparatus as in claim 3, wherein the wall segment is in thermal contact with an outer wall of the combustion chamber.
 6. The driving apparatus as in claim 1, wherein the thermally conductive element comprises a wall segment, which extends inwardly from an outer wall of the injection line.
 7. The driving apparatus as in claim 6, wherein the wall segment extends along a direction of flow of the combustion gas in the injection line.
 8. The driving apparatus as in claim 6, wherein the injection line has two flow chambers for the fuel and the wall segment separates the two flow chambers from each other.
 9. The driving apparatus as in claim 1, wherein the injection line has at least in a segment a plurality of hydraulically and/or geometrically parallel branch lines.
 10. The driving apparatus as in claim 9, wherein at least two of the branch lines are configured as separate positioned lines.
 11. The driving apparatus as in claim 10, wherein at least one of the separate branch lines is in thermal contact with an outer wall of the combustion chamber.
 12. The driving apparatus as in claim 10, wherein the separate branch lines open into the combustion chamber at points that are separate from each other.
 13. The driving apparatus as in claim 12, wherein jets of fuel injected into the combustion chamber from the branch lines cross.
 14. The driving apparatus as in claim 1, wherein the thermal conductive element comprises a material with a thermal conductivity of more than 70 W/(m·K).
 15. The driving apparatus as in claim 1, wherein the thermal conductive element is arranged downstream from the valve element.
 16. The driving apparatus as in claim 2, wherein the injection line contacts the outer wall of the combustion chamber.
 17. The driving apparatus as in claim 2, wherein the thermally conductive element comprises a wall segment, which extends outwardly from an outer wall of the injection line.
 18. The driving apparatus of claim 5, wherein the wall segment contacts the outer wall of the combustion chamber.
 19. The driving apparatus as in claim 17, wherein the wall segment extends along the injection line.
 20. The driving apparatus as in claim 4, wherein the wall segment is in thermal contact with an outer wall of the combustion chamber. 